You have asked a very good question focussing on characterisation of the two main characters in the gang. What is interesting about Trevor is that we are not given access as readers to any of his thoughts, so we have to infer his motives for organising and accomplishing the destruction of Old Misery's House. He is clearly a dynamic character in that he provides the initiative and the plan and the energy to mobilise and organise the gang in order to destroy the house. Yet he is also clearly emotionally disturbed and detached from everyone and everything around him. Consider the following quote:
"All this hate and love," he said, "it's soft, it's hooey. There's only things, Blackie," and he looked round the room crowded with the unfamiliar shadows of half things, broken things, former things.
Trevor is a character who is so emotionally divorced from the world that he destroys without passion and is not able to feel emotion. Thus to him, the destruction is actually an act of creation as it expresses his nihilistic attitude towards the world and his rejection of everything that the world values.
Blackie is perhaps a simpler character, the initial leader of the gang who resumes his post of leadership towards the end of the story. When T. usurps his leadership, initially he is annoyed and "dimly aware of the fickleness of favour", but then, thinking of the fame this endeavour could gain for the gang, he is quite willing to return and become a member of the gang under T's leadership in order to achieve this feat:
Driven by the pure, simple, and altruistic ambition of fame for the gang, Blackie came back to where T. stood in the shadow of Misery's wall.
Blackie is not so focussed on power that he is not willing to be a part of this scheme, but it is clear from his conversations with T. that he does not fully understand or share T.'s nihilistic outlook on the world.